Because of the increasing shortage of raw material resources and the raw material price increases resulting therefrom, processes for working up plastic consumer articles which are no longer useful, in the sense of recovery either of starting substances or the original plastic directly, are becoming more and more important.
Thus, in German Democratic Republic Patent Specification Nos. 45,575, 46,282, 45,599, 45,600 and 46,353, E. Bullack describes a process for the working up of polycarbonates, in particular with regard to the isolation of 4,4'-dihydroxy-diaryl-alkanes as starting substances for polycarbonate syntheses.
According to German Democratic Republic Patent Specification Nos. 45,575, 46,282 and 45,599, the 4,4'-dihydroxy-diaryl-alkanes are obtained, after purification processes which in some cases are expensive, via cleavage by means of alcohols, acid anhydrides or small amounts of basic catalysts. According to Patent Specification Nos. 45,600 and 46,353, the cleavage is achieved by adding phenols or diaryl carbonates in the presence of metal oxide catalysts at temperatures above 180.degree. C. There is the danger of side reactions at these temperatures, especially if metal oxide catalysts are present, and extensive purification operations are necessary in order to isolate clean starting substances.